MGC3140 datasheet(9/49 Pages) MICROCHIP

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Theory of Operation: Electrical Near-Field (E-Field) Sensing

Microchip’s GestIC technology is a 3D sensor technology which utilizes an electric field (E-field) for

advanced proximity sensing. It allows realization of new user interface applications by detection, tracking

and classification of a user’s hand gestures in free space.

E-fields are generated by electrical charges and propagate three-dimensionally around the surface,

carrying the electrical charge.

Applying direct voltages (DC) to an electrode results in a constant electric field. Applying alternating

voltages (AC) makes the charges vary over time and, thus, the field. When the charge varies sinusoidally

with frequency ‘f’, the resulting electromagnetic wave is characterized by wavelength λ = c/f, where ‘c’ is

the wave propagation velocity — in vacuum, the speed of light. In cases where the wavelength is much

larger than the electrode geometry, the magnetic component is practically zero and no wave propagation

takes place. The result is quasi-static electrical near field that can be used for sensing conductive objects

such as the human body.

Microchip’s GestIC technology uses five transmit (Tx) frequencies, 42, 43, 44, 45 and 100 kHz, with

wavelengths of at least three kilometers. This wavelength is much larger than the typical range of

electrode dimensions between 5 mm and 20 mm. GestIC systems work without wave propagation.

In case a person’s hand or finger intrudes the electrical field, the field becomes distorted. The field lines

are drawn to the hand due to the conductivity of the human body itself and shunted to ground. The 3D

electric field decreases locally. Microchip’s GestIC technology uses a minimum number of four receiver

(Rx) electrodes to detect the E-field variations at different positions to measure the origin of the electric

field distortion from the varying signals received. The information is used to calculate the position, track

movements and classify movement patterns (gestures).

The two following figures show the influence of an earth-grounded body to the electric field. The proximity

of the body causes a compression of the equipotential lines and shifts the Rx electrode signal levels to a

lower potential which is measured.

Figure 3-1. Equipotential Lines of an Undistorted E-Field

MGC3140

Theory of Operation: Electrical Near-Field (E-Fiel...

DS40002037A-page 9

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